Those interested in physics-based simulation of snowflake growth should have a look at this page [1] with papers describing models to do so, in particular part II describes a two-dimensional model, part III a three-dimensional model. There also many rendered images and a couple of videos of the simulation results and even some code.
A lot of information can also be found on Kenneth G. Libbrecht's snowcrystals.com [2] including many snowflake photographs. Also the photographs of Alexey Kljatov [3] are quite well known.
[1] http://psoup.math.wisc.edu/Snowfakes.htm
[2] http://snowcrystals.com
[3] https://alexey-kljatov.pixels.com